Separation methods for water treatment include a method using a filtering membrane, a method using heat or phase-change, and so on.
A separation method using a filtering membrane has a lot of advantages over the method using heat or phase-change. Among the advantages is the high reliability of water treatment since the water of desired purity can be easily and stably obtained by adjusting the size of the pores of the filtering membrane. Furthermore, since the separation method using a filtering membrane does not require a heating process, the method can be used together with microorganisms which are useful for separation process but might be adversely affected by heat.
Among the separation methods using a filtering membrane is a method using a hollow fiber membrane module comprising a bundle of hollow fiber membranes. Typically, a hollow fiber membrane module has been widely used in the field of microfiltration and/or ultrafiltration for obtaining axenic water, drinking water, super pure water, and so on. Recently, the application of the hollow fiber membrane module is extended to wastewater treatment, solid-liquid separation in a septic tank, removal of suspended solid (SS) from industrial wastewater, filtration of river, filtration of industrial water, filtration of swimming pool water, and the like.
A filtration system using hollow fiber membranes may be classified into a submerged-type filtration system and a pressurized-type filtration system according to the operation manner thereof.
FIG. 1 schematically shows a submerged-type filtration system of the prior art.
As shown in FIG. 1, the submerged-type filtration system of the prior art comprises a processing tank 10. Typically, the processing tank 10 is disposed below the surface of the ground and is a open-type tank whose inside is exposed to the external environment through the upper portion thereof.
A filtering apparatus 20 is disposed in the processing tank. The filtering apparatus 20 comprises a plurality of hollow fiber membranes.
The feed water to be treated is supplied from the feed water tank 30 to the processing tank 10 by means of the first pump P1. The filtering apparatus 20 is sufficiently submerged into the feed water supplied from the feed water tank 30, and then the second pump P2 provides the filtering apparatus 20 with the negative pressure.
More particularly speaking, the lumen of the hollow fiber membrane of the filtering apparatus becomes a vacuum state as the negative pressure is applied thereto by the pump P2, which makes only the pure water other than the impurities (hereinafter, “permeate”) pass through the hollow fiber membrane and enter the lumen thereof. Then, owing to the negative pressure continuously provided by the second pump P2, the permeate introduced in the lumen of the hollow fiber membrane is forwarded to the permeate tank 40.
According to the submerged-type filtration system of the prior art, however, the amount of the energy consumed by the second pump P2 for making the lumen of the hollow fiber membrane into a vacuum state and forwarding the permeate introduced in the lumen to the permeate tank 40 is enormous.
Thus, it is strongly required to find a way to reduce the amount of the energy for the operation of the submerged-type filtration system.